As compared with a conventional flat sputtering target, a cylindrical (also referred to as “rotary” or “rotatable”) sputtering target has an advantage of having a higher use efficiency because a sputtering target member thereof has an entire surface thereof eroded and thus is shaven uniformly. Therefore, the conventional flat sputtering target is now being replaced with the cylindrical sputtering target.
According to a known manufacturing method of a cylindrical sputtering target, a cylindrical sputtering target member is formed by thermal spraying on an outer circumferential surface of a cylindrical substrate, so that the cylindrical sputtering target member and the cylindrical substrate are integrated. According to another known manufacturing method of a cylindrical sputtering target, a cylindrical sputtering target member formed of a ceramic sintered compact separately formed is joined to a cylindrical substrate by use of a joining material such as a solder material or the like. In an example of the latter manufacturing method, a powdery material of a cylindrical sputtering target member is put on an outer circumferential surface of a cylindrical substrate and subjected to hot isostatic pressing (HIP).
With the method of integrating a cylindrical sputtering target member and a cylindrical substrate to manufacture a cylindrical sputtering target, it is difficult and uneconomical to reuse the cylindrical substrate. In addition, the cylindrical sputtering target member is cracked or chipped off at the time of sputtering due to a difference in the coefficient of thermal expansion between the cylindrical sputtering target member and the cylindrical substrate.
By contrast, with the method of joining a cylindrical sputtering target member formed of a ceramic sintered compact separately formed to a cylindrical substrate by use of a joining material such as a solder material or the like, the joining material such as a solder material or the like is provided between the cylindrical sputtering target member and the cylindrical substrate. Therefore, in the case where the space between the cylindrical sputtering target member and the cylindrical substrate is not sufficiently fulfilled with the joining material such as a solder material or the like, the joining performance is insufficient.
In the case where the joining performance is insufficient, the cylindrical sputtering target member, which is expanded at the time of sputtering, comes off from the cylindrical substrate and rotates idle, or the cylindrical sputtering target member is cracked or chipped off.
In order to join the cylindrical sputtering target member and the cylindrical substrate more strongly, Japanese Laid-Open Patent Publication No. 2010-18883 discloses the following: a cavity between the cylindrical sputtering target member and the cylindrical substrate is filled with a joining material such as a solder material or the like; the cylindrical sputtering target member, the cylindrical substrate and the joining material are cooled in an axial direction from one end thereof toward the other end thereof; and the joining material in a melted state is further supplied during the cooling. The joining material is supplied in this manner so as to improve the joining state and thus prevent the cylindrical sputtering target member from being cracked or chipped off.
Usually, a joining material such as a solder material or the like is provided in a liquid state to fill the cavity between the cylindrical sputtering target member and the cylindrical substrate. While being cooled after filling the cavity, the joining material is changed into a solid state to join the cylindrical sputtering target member and the cylindrical substrate to each other. In consideration of the amount of thermal contraction of the joining material that is caused by the cooling, the method disclosed in Japanese Laid-Open Patent Publication No. 2010-18883 is regarded as improving the ratio of the joining material filling the cavity by further supplying the joining material in such an amount that compensates for the amount of thermal contraction of the joining material.
However, the method disclosed in Japanese Laid-Open Patent Publication No. 2010-18883 merely compensates for the amount of thermal contraction of the joining material. Therefore, the method disclosed in this publication prevents the joining performance of the joining material merely in the axial direction of the cylindrical sputtering target member from being reduced due to the contraction at the time of cooling.
Regarding the contraction of the joining material, the contraction in a diametrical direction of the cylindrical sputtering target member needs to be considered as well as the contraction in the axial direction. A reason for this is that the cylindrical substrate and the cylindrical sputtering target member are easily delaminated from each other by the contraction of the joining material in the diametrical direction of the cylindrical sputtering target member. Even in the case where the cooling in the axial direction is started from the one end and the joining material in a melted state is supplied to the cavity, it is difficult to perform control such that the cavity does not include a space, which may be formed due to the contraction of the joining material in the diametrical direction of the cylindrical sputtering target member. A reason for this is that the joining material has a certain level of viscosity. Japanese Laid-Open Patent Publication No. 2010-18883 does not take a measure against a space formed, between the cylindrical sputtering target member and the joining material, due to the contraction of the joining material in the diametrical direction of the cylindrical sputtering target member.
The present invention has an object of providing a cylindrical sputtering target that has an improved joining performance between the cylindrical sputtering target member and the cylindrical substrate and prevents the cylindrical sputtering target member from being cracked of chipped off at the time of sputtering due to the difference in the coefficient of thermal expansion between the cylindrical sputtering target member and the cylindrical substrate, and a manufacturing method of the same.